In industrial process measurements technology, especially also in connection with the automation of chemical processes or processes adding value to materials, process-near measuring systems are used for registering process-describing, measured variables and for producing measured value signals representing such. These process-near measuring systems are applied directly to, or in, a process line, through which medium is flowing. The measured variables to be registered include, for example, mass- and/or volume flow, e.g. flow rate, flow velocity, density, viscosity, electrical conductivity, temperature, and the like, of a liquid, powdered, vaporous, or gaseous, process medium, which is conveyed, or held, in a process line embodied, for example, as a pipeline.
The measuring systems can be, for example, such wherein in-line measuring devices working with magneto-inductive, measuring transducers or transducers evaluating travel time of ultrasonic waves emitted in the flow direction, especially also those working according to the Doppler principle, are used. Examples developing these ideas further for such measuring systems, examples known per se to those skilled in the art, especially measuring systems formed by means of compact measuring devices, are described in detail in, among others, EP-A 1 039 269, EP-A 984 248, GB-A 21 42 725, U.S. Pat. Nos. 4,308,754, 4,420,983, 4,468,971, 4,524,610, 4,563,904, 4,716,770, 4,768,384, 4,787,252, 5,052,229, 5,052,230, 5,131,279, 5,231,884, 5,531,124, 5,351,554, 5,359,881, 5,458,005, 5,463,905, 5,469,748, 5,540,103, 5,687,100, 5,796,011, 5,808,209, 6,003,384, 6,053,054, 6,031,740, 6,006,609 6,189,389, 6,257,071, 6,293,156, 6,352,000, 6,397,683, 6,330,831, 6,513,393, 6,644,132, 6,651,513, 6,880,410, 6,910,387, US-A 2005/0092101, US-A 2006/0010991, WO-A 88/02 476, WO-A 88/02 853, WO-A 95/16 897, WO-A 00/36 379, WO-A 00/14 485, WO-A 01/02 816, or WO-A 02/086 426.
For registering the respective measured variables, measuring systems of the type discussed here usually include a corresponding measuring transducer, which is, for example, inserted into the course of a process line conveying a medium, or into a wall of a container containing the medium, and serves for producing at least one measurement signal, especially an electrical measurement signal, representing, as accurately as possible, the primarily registered, measured variable. For this, measuring transducers of in-line measuring devices are equipped, for example, with a measuring tube inserted into the course of the relevant process line, such that the medium can be conveyed through the measuring tube. Additionally, measuring transducers of in-line measuring devices are equipped with a corresponding physical-to-electrical sensor arrangement. The sensor arrangement, in turn, includes at least one sensor element reacting primarily to the measured variable to be registered or also to changes of the same, by means of which at least one measurement signal correspondingly influenced by the measured variable is produced. For further processing or evaluating the at least one measurement signal, the measuring transducer is further connected with a measuring electronics correspondingly suited therefor.
The measuring electronics, communicating in suitable manner with the measuring transducer, produces, during operation of the measurement system, with application of the at least one measurement signal, at least at times, at least one measured value instantaneously representing the measured variable, thus, for instance, a mass flow measured value, a volume flow measured value, a density measured value, a viscosity measured value, a pressure measured value, a temperature measured value, or the like.
Commercial flow transducers are usually implemented as pre-fabricated and pre-calibrated components having a carrier tube insertable into the course of the pertinent process line, as well as at least one physical-to-electrical, transducer element appropriately premounted thereon, with the latter, on occasion in conjunction with the carrier tube itself and/or other components of the flow transducer, especially passive-invasive components, such as e.g. flow obstacles protruding into the flow, and/or active components of the flow transducer, such as e.g. magnetic field producing, coil arrangements placed externally on the carrier tube, or sound generating transducers, forming the at least one flow sensor delivering the measurement signal. Widely distributed in industrial measurements technology are, especially, magneto-inductive flow transducers, flow transducers evaluating the travel time of ultrasonic waves coupled into flowing medium, eddy flow transducers, especially vortex flow transducers, flow transducers with oscillating measuring tube, flow transducers evaluating pressure differences, or thermal flow measuring transducers.
By means of in-line measuring devices having a magneto-inductive transducer, for instance, flow velocity and/or volume flow of an electrically conductive, liquid medium flowing through a measuring tube of the measuring transducer in a flow direction can be measured. To this end, there is produced in the magneto-inductive transducer, by means of diametrally opposed field coils of a magnetic circuit arrangement electrically connected to an exciter electronics, a magnetic field, which passes through the medium within a predetermined measuring volume at least sectionally perpendicularly to the flow direction and which closes on itself essentially outside of the medium. The measuring tube is made, therefore, usually of non-ferromagnetic material, in order that the magnetic field not be unfavorably affected during measuring. As a result of the movement of the free charge carriers of the medium in the magnetic field, an electric field is produced in the measuring volume according to the magneto-hydrodynamic principle. The electric field extends perpendicularly to the magnetic field and perpendicularly to the flow direction of the medium. By means of at least two measuring electrodes arranged spaced from one another in the direction of the electric field and by means of an evaluating electronics of the in-line measuring device connected to the measuring electrodes, an electric voltage induced in the flowing medium is then measurable and, in turn, provides a measure for the volume flow. Measuring electrodes, for example, either galvanic electrodes contacting the medium or capacitive electrodes not contacting the medium, can serve for sensing the induced voltage. For conveying and coupling of the magnetic field into the measuring volume, the magnetic circuit arrangement usually includes coil cores surrounded by the field coils and spaced from one another along a periphery of the measuring tube, especially diametrally spaced, and, having free, terminal faces arranged with respect to one another, especially as if they are mirror images of one another. During operation, thus, the magnetic field produced by means of the field coils connected to the exciter electronics is coupled via the coil cores into the measuring tube in such a manner that the magnetic field passes through the medium flowing between the two terminal faces at least sectionally perpendicularly to the flow direction. In addition to volume flow, or flow velocity, also the electrical conductivity of the fluid can be determined by means of modern in-line measuring devices equipped with a magneto-inductive transducer. As an alternative to in-line measuring devices with magneto-inductive measuring transducers, often also in-line measuring devices measuring acoustically by means of ultrasound are used for measuring flow velocities and/or volume flows of flowing media.
Basic construction and functioning of magneto-inductive flow transducers are disclosed e.g. in EP-A 1 039 269, U.S. Pat. Nos. 6,031,740, 5,540,103, 5,351,554, 4,563,904, while the same for ultrasonic flow transducers is disclosed e.g. in U.S. Pat. Nos. 6,397,683, 6,330,831, 6,293,156, 6,189,389, 5,531,124, 5,463,905, 5,131,279, 4,787,252. Since also the others of the above mentioned measuring principles usually employed in industrial flow measuring transducers are likewise sufficiently know to those skilled in the art, further detailing of these as well as also other principles of measurement established in industrial measurements technology and implemented by means of flow measuring transducers is not necessary.
Due to the high integrity as well as form-stability required for such measuring tubes, they are made, both in the case of measuring transducers measuring magneto-inductively as well as also acoustically or, on occasion, also in the case of measuring transducers working according to other principles of measurement, most often of an outer support tube, especially a metal support tube, of predeterminable strength and size, lined internally with an electrically non-conductive, insulating material of predeterminable thickness, the so-called liner. For example, in U.S. Pat. Nos. 6,595,069, 5,664,315, 5,280,727, 4,679,442, 4,253,340, 3,213,685 or JP-Y 53-51 181, in each case, magneto-inductive measuring transducers are described, which include a measuring tube which can be joined fluid-tightly into the course of a pipeline. The measuring tube has an inlet-side, first end and an outlet-side, second end and is composed of a non-ferromagnetic support tube as the outer jacket of the measuring tube, and a tubular liner of an insulating material accommodated in a lumen of the support tube for conveying a flow medium isolated from the support tube.
The liner, which is usually of a thermoplastic, thermosetting or elastomeric, synthetic material, or plastic, serves for chemically isolating the support tube from the medium. In the case of magneto-inductive measuring transducers, in which the support tube has a high electrical conductivity, for example in the case of application of metal support tubes, the liner serves, furthermore, as electrical insulation between the support tube and the medium for preventing a short circuiting of the electric field via the support tube. By a corresponding design of the support tube, as a result, thus a matching of the strength of the measuring tube to the mechanical loading present in the particular application is realizable, while, by means of the liner, a matching of the measuring tube to the chemical and/or biological demands associated with the particular application can be realized.
A special problem of the aforementioned measuring devices is that, among other things, they can, most often, only be disposed of with much difficulty, following their removal from use. This is especially true, because measuring devices of the type discussed here are made, as already mentioned, usually to a considerable extent of synthetic materials. Especially in the case of in-line measuring devices having contact surfaces of plastics for contacting the measured medium mentioned at the start hereof, such as, for example, in-line measuring devices with magneto-inductive measuring transducers, such plastics are, on the one hand, because of the conditions under which they serve in use, made to be inert relative to a large number of chemical compounds, and, as a result, are also, according to the specified use, equally difficultly decomposable chemically. On the other hand, plastics used in conventional measuring devices, especially also as a result of, on occasion, disadvantageous combining with contaminants not directly removable, such as, perhaps resulting from formation of deposits and/or diffusion, must frequently be treated as hazardous waste and are, as a result, only conditionally recyclable or can be destroyed or terminally deposited only with very complicated safety measures.